1. Field of the Invention
The present invention relates to image forming devices and image forming methods for outputting onto print data an image that additional data is embedded.
2. Description of the Related Art
Recently, a technique has been developed for improving the value of a printout itself by adding a special pattern, such as a copy-forgery-inhibited pattern (a texture pattern), an electronic watermark, or an Anoto (registered trademark) pattern, to a printout, and has been implemented in image forming devices.
The texture pattern comprises a latent image pattern constituting a latent image portion, which appears on reproduction and is output, and a background pattern constituting a background portion whose dot disappears on reproduction. By generating (creating) a printout (printed material) wherein a combination of these patterns is superimposed over or under an image desired to be printed, the latent image pattern appears when attempting to reproduce this printout.
In the case of the electronic watermark, a printout is generated by adding a pattern, in which meaningful information is embedded, to an image to be printed. By analyzing the pattern when this printout is scanned, the embedded information can be extracted and used as electronic information.
The Anoto pattern is one of electronic watermark which Anoto Group AB of Sweden has developed, and is a pattern where positional information on a paper is embedded.
The processing when these special patterns are sent together with print data as PDL data from a host to a printer is described below.
The printer generates intermediate data from this PDL data first, and stores the intermediate data into an intermediate data storage buffer. Once all of the intermediate data are stored, the intermediate data are rasterized, and an image is generated and printed (i.e., a printed material is prepared).
However, the data amount of the intermediate data may be large and thus the intermediate data storage buffer may be filled. In such a case, a fallback processing is performed in the conventional art.
The fallback processing is a processing, in which in the middle of generating intermediate data and storing the data into a buffer, the intermediate data stored in the intermediate data storage buffer is rendered once and subjected to JPEG compression. It is needless to say that when this processing is performed, the intermediate data ended midway will be deleted from the buffer.
Thus, a space is made in the intermediate data storage buffer, so that the intermediate data subsequently generated can be stored in the intermediate data storage buffer. Although it looks everything works well here, there is also a problem, which is in JPEG compression.
The special pattern is a pattern without periodicity, the on/off of which is frequently repeated. An image of such a pattern has many high frequency components as compared with an ordinary natural image or a graphic image, and therefore even if it is compressed by JPEG compression, the data amount cannot be significantly reduced. It is needless to say there is one idea that in order to reduce the data amount, the compression is performed with an increased compression ratio, but in such a case, image degradation becomes severe and the functionality as a texture pattern, an electronic watermark, or an Anoto pattern will degrade or otherwise will not work at all.
In order to avoid such a problem, Japanese Patent Laid-Open No. 2002-127409 discloses a method for applying a lossless compression, not the lossy compression such as JPEG compression, to print data including the special pattern.
On the other hand, as in Japanese Patent Laid-Open No. 2002-127409, if an image including the special pattern is subject to a lossless compression, the size of the compressed image will increase. As a result, in order to store the compressed image, a memory larger than the one in the case where JPEG compression is performed needs to be prepared.